Saturday, March 26, 2005

Obesity and Life Span

Last week's New England Journal of Medicine contained a "Special Report" that rising obesity will eventually lead to reduced lifespan (unfortunately only available to subscribers; I think it's near criminal that NEJM publishes this kind of deliberately provocative article about and then doesn't make it available to the public):

Obesity could shorten the average lifespan of an entire generation — today's children — by two to five years, according to a controversial new life-expectancy analysis.

Obesity has been shown to have a substantial negative effect on longevity, reducing the length of life of people who are severely obese by an estimated 5 to 20 years

Will this happen? I can't be sure, but the arguments presented are remarkably weak. Basically, the authors argue that obesity is such a problem that it will overwhelm progress in other areas of health care and lead to declining life-expectancy.

Obesity has been shown to have a substantial negative effect on longevity, reducing the length of life of people who are severely obese by an estimated 5 to 20 years

So far so good. Everyone agrees obesity is bad. I'm sure almost everyone would agree that worsening obesity is likely to be a drag on life expectancy. The striking rise in diabetes, which primarily affects the overweight and inactive (this is type 2 or Adult onset Diabetes, not type 1 which usually starts young) is noted

From 1979 to 1999, rates of death from diabetes increased annually by an average of 2.8 percent for males and 1.8 percent for females. In 1990, diabetes decreased life expectancy by 0.22 year for males and 0.31 year for females, 40 but the negative effect of diabetes on life expectancy has grown rapidly since then. However, the negative effect of diabetes on the life expectancy of the population could now be several times as great as it was in 1990.

Terrifying, huh. It is until you think about why more people are dying of diabetes. The main one is they aren't dying of anything else. Advancements in treatment of cancer and, especially, treatment and PREVENTION of cardiovascular disease have mean a lot less people are dying of those. Hell, you've got to die of something. The decreasing mortality from heart disease is particularly notable because obesity is a risk for developing cardiovascular disease, as is diabetes

But that is not all. There is a lot more badness coming:

There are other realistic threats to increases in life expectancy. From 1980 to 1992 in the United States, the age-adjusted rate of death from infectious diseases rose by 39 percent, an increase fueled mostly by the AIDS epidemic;

but that's not all:

Other forces that could attenuate the rise in life expectancyinclude pollution, lack of regular exercise, ineffective blood-pressure screening, tobacco use, and stress.

If AIDS and obesity don't get you, ineffective blood-pressure screening will. With all this bad news, I'm almost surprised life-expectancy isn't falling already. But it isn't, is it? And in that observation lies the fatal flaw in the studies' reasoning.

Guess what? People are getting fatter, but they've been getting fatter for a while now. AIDS has been around for a while, etc. All these factors are already factored in when actuaries make projections about future life expectancy. As Samuel Preston put it in an accompanying editorial, that would be devastating if it weren't so darn nice:

The effect of an increase in the prevalence and severity of obesity on the longevity of U.S. citizens is already embedded in extrapolated forecasts made in recent periods. In fact, these forecasts implicitly assume that the severity of obesity will continue to worsen, and the prevalence will rise, since it is the rate of change in the determinants of mortality, rather than the level, that drives projected changes in life expectancy.

So, obesity is getting worse, but many other things are getting better and there is no reason to think obesity will suddenly overwhelm all the positive developments, like better treatements for AIDS, cancer, diabetes, etc. Of course, there is also the very real possibility that effective treatments for obesity itself will come about. Whether via lifestyle changes or a pill that increases metabolism, this is a real possibility.

Never underestimate the possibility for medicial progress. 8 years ago, someone I know well was in the hospital with Pneumocystis pneumonia, a CD4 count in the double digits and HIV throughout his body. Today he works, takes medicines and lives his life. Think about that.

Could an avian flu epidemic decimate the world. Maybe, but I doubt it. Anti-viral medicines are already being stockpiled in rich countries, work on a vaccine is progressing and the experience with SARS gives public health officials crucial experience in containing outbreaks of infectious disease. AIDS has been a drag on life expectancy, but hasn't caused it to go down (at least in the US, Africa is a different story)

Lost in the alarmism, is the point that obesity is a large and growing (sorry) problem for the health of Americans. I agree with this. It deserves money and attention, as do avian flu, cancer, heart disease, etc. It is a drag on life expectancy, but it is hardly the only factor.

7 Comments:

May I add that if the goalposts stopped moving we might be better off? A few years ago, I was obese - since then I have lost fifty pounds and find myself classed as "morbidly" obese. Throughout, I've considered myself "vey fat" down to just "fat."

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